1. Field of the Invention
This invention relates to intramedullary nails for use in fracture management. More particularly, this invention relates to placement of locking members in intramedullary nails by improved intraoperative distal targeting.
2. Description of the Related Art
Since the development of intramedullary nails for use in orthopedic surgery to manage bone fractures, it has been common practice to fix the bone with respect to the nail by placing locking members through holes drilled through cortical bone in alignment with holes that are pre-drilled transversely in the nail. The procedure has presented technical difficulties, as the pre-drilled holes in the nail are not generally visible to the surgeon, and are difficult to localize and to align with surgical drills and placement instruments, so as to receive the locking members.
Placement of the holes in the cortical bone under X-ray or fluoroscopic guidance has been undertaken in the past, often in combination with complex mechanical alignment devices such C-arms, and stereotactic frames. This approach has proven to be unsatisfactory, due to difficulties in obtaining precise alignment, and maintaining alignment without unduly increasing radiation exposure of the operator, other operating room personnel, and the patient. Attempts to limit radiation exposure by offsetting the drill from the X-ray beam have also not been entirely successful. The use of such procedures has often extended operating time and has increased operative risk and mortality.
Sensors have long been employed to aid in positioning surgical instruments and manipulators. For example, in U.S. Pat. No. 5,279,309, it is proposed to place light emitting beacons on a patient's body in order to establish a frame of reference to locate the relative position of a sensor relative to the beacons in three dimensions. This disclosure is advantageous in situations where direct vision is possible, for example, for robotic manipulators.
More recently magnetic field sensors have been employed in conjunction with intramedullary nails in order to improve localization of the locking holes, and alignment of the locking members.
The patent document WO 93/02626 proposes the use of two or more magnetic driver coils inside a probe that is insertable into a hollow splint such as a nail. A yoke having detection coils on opposite sides of the splint detects the magnetic fields. A maximum signal indicates alignment with a hole in the splint.
The patent document WO 97/13467 discloses the fixation of two electromagnetic drivers in a rod, which is then introduced along an intramedullary nail. In a variation of this arrangement, a neodymium magnet is positioned on the rod, or as plugs to the nail hole. A detector having four coils is used to determine the direction the probe needs to move in order to be centered on the nail hole. Use of a second detector, disposed at a 45-degree angle to the first, permits 3-dimensional localization of the probe.
U.S. Pat. No. 5,411,503 discloses the use of a probe, which is insertable into an intramedullary nail after a fracture has been reduced and the nail has been implanted. A hand-held guide moved about by the surgeon is used to achieve and maintain the proper alignment of a drill or other instrument used in the placement of transverse locking screws. A display unit, connected by electronic cables to the probe and guide, presents visual images that graphically indicate the manner in which the guide must be moved to bring it into proper alignment. Two orthogonal electromagnetic drive coils are embedded near one end of the nail, each having a magnetic axis in parallel alignment with, and at a fixed distance from the axis of a transverse hole. The coils are intermittently driven in non-overlapping time intervals. Multiple receiving coils or Hall effect transducers are placed in the guide, and alignment of the guide is indicated by null signals.
U.S. Pat. No. 5,127,913 proposes to dispose neodymium magnets in a probe that is inserted in the hollow interior of an intramedullary nail. The probe carries a plurality of high-energy magnets having magnetic poles oriented along an axis transverse to a longitudinal axis of the probe, and concentric with an axis of the distal locking holes of the intramedullary nail. An indicator aligns the insert member and the magnets at an aligned position so that the axes of the magnets and distal locking holes are aligned. A single detector magnet for detecting a magnetic field generated by the aligned high-energy magnets through the distal locking holes is disposed exterior to the bone, enabling the operator to mark the location of the locking holes. This arrangement does not provide an indication of a desired direction to move a surgical tool, and is relatively insensitive to deviations when the tool is near an optimum location.
In U.S. Pat. No. 5,584,838 an arrangement is proposed for generating a magnetic field within an intramedullary nail, which has a maximum strength along an axis of a transverse locking hole, and which decreases in strength in directions radially away from the axis. A drill guide has two mounted sensor arrangements at axially spaced locations, each of which has a plurality of sensors at angularly spaced locations, and spaced radially from an opening through the drill guide. This arrangement is responsive to a deviation of the drill opening in the drill guide from coaxial alignment with the axis of the locking hole, and provides a perceptible indication of a radial direction from the drill opening to the axis.
U.S. Pat. No. 6,074,394 proposes using a targeting device having at least two magnetic field communication units to achieve distal targeting. The device consists of a receiver and a transmitter producing multi-axis pulsed direct current magnetic signals in each of three orthogonal planes. One of the communication units is carried in a fixed position by a drill guide and a second of the communication units is in a fixed, offset position relative to an implant connector. The position and orientation of the drill guide relative to the implant connector are determined by the transmission of the pulsed direct current magnetic signal from the transmitting unit and receiving that signal at the receiver. The signals provide the position and location of the communication units in relation to one another. Alignment of the drill guide with the connector is aided by viewing a virtual representation of the position and orientation of the connector and drill guide on a console having a fixed location. This arrangement is somewhat inconvenient for the operator, as it is continually necessary to reference the display, or to obtain callouts from an assistant viewing the fixed console.